a. Field of the Invention
The invention relates to high-tenacity wholly aromatic polyamide fiber and film having a very high modulus and a process for the preparation thereof.
b. Description of the Prior Art
It is known that wholly aromatic polyamides have a high melting point and a high glass transition point and they are excellent in physical and chemical properties such as heat resistance, flame resistance, flame retardancy and chemical resistance. Accordingly, they are very valuable as various shaped articles such as fibers and films. It also is known that among wholly aromatic polyamides, a para-oriented polymer, for example, poly(p-phenylene terephthalamide), gives a fiber or film having especially high tenacity and a high modulus. Such high-tenacity and high-modulus shaped articles have widely been used as industrial materials.
In the field of industrial materials, wholly aromatic polyamide shaped articles having further improved characteristics have been desired under the stimulus of the above-mentioned high-tenacity and high-modulus fibers. More specifically, high-tenacity wholly aromatic polyamide fibers are now desired mainly as fibers for reinforcing light communication cables or ropes to be used for special purposes.
In high-tenacity high-modulus wholly aromatic polyamides which have been marketed and are now being developed, the modulus is about 300 to about 550 g/d. It is said that the modulus that should be possessed by high-capacity wholly aromatic polyamide fibers which are eagerly desired at present is at least 650 g/d, preferably at least 700 g/d.
As a fiber having such a very high modulus, there can be mentioned Kevlar-49 manufactured and supplied by Du Pont Co. This Kevlar-49 is prepared through the following spinning and heat treatment steps.
1. Spinning
A high-concentration liquid crystal dope comprising poly-(p-phenylene terephthalamide) and sulfuric acid is subjected to dry-jet wet spinning using water or dilute sulfuric acid as a coagulating bath (see Japanese Patent Publication No. 14,170/80).
2. Heat Treatment
The as-spun filaments formed by the above dry-jet wet spinning is heat-treated under tension at 250.degree. to 600.degree. C. (see Japanese Patent Publication No. 14,167/80).
In this process, however, sulfuric acid which is very dangerous and highly corrosive is used as a solvent and special steps of isolating, washing and drying the polymer and dissolving the dried polymer into concentrated sulfuric acid are inevitably adopted.
Preparation of a spinning dope by forming a polymer solution by low temperature solution polymerization of an aromatic diamine and an aromatic diacid chloride in an amide type polar solvent and neutralizing hydrogen chloride formed as a by-product with, for example, Ca(OH).sub.2, has already been practiced for production of meta-oriented polyamide shaped articles (see Japanese Patent Publication No. 16,027/60). Furthermore, a process in which the above method is applied to the preparation of para-oriented polyamides obtained from a combination of specific monomers and the resulting spinning dope is subjected to wet spinning and hot drawing to obtain high modulus fibers having a modulus of at least 300 g/d has already been proposed (see Japanese Patent Application Laid-Open Specification No. 136,916/76).